Abiotic Stress Signaling and Responses in Plants.

The responses of plants to stress factors are extremely elaborate [...].

Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites.

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.

Differential Water Deficit in Leaves Is a Principal Factor Modifying Barley Response to Drought Stress.

In response to environmental stress, plants activate complex signalling, including being dependent on reactive oxygen-nitrogen-sulphur species. One of the key abiotic stresses is drought. As a result of drought, changes in the level of hydration of the plant occur, which obviously entails various metabolic alternations. The primary aim of this study was to determine the relationship between the response of barley to drought and the intensity of stress, therefore investigations were performed under various levels of water saturation deficit (WSD) in leaves at 15%, 30%, and 50%. In barley subjected to drought, most significant changes occurred under a slight dehydration level at 15%. It was observed that the gene expression of 9-cis-epoxycarotenoid dioxygenases, enzymes involved in ABA biosynthesis, increased significantly, and led to a higher concentration of ABA. This was most likely the result of an increase in the gene expression and enzyme activity of L-cysteine desulfhydrase, which is responsible for H2S synthesis. Our results suggest that the differential water deficit in leaves underlies the activation of an appropriate defence, with ABA metabolism at the centre of these processes. Furthermore, at 15% WSD, a dominant contribution of H2O2-dependent signalling was noted, but at 30% and 50% WSD, significant NO-dependent signalling occurred.

The Alleviation of Metal Stress Nuisance for Plants-A Review of Promising Solutions in the Face of Environmental Challenges.

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance.

PYR/PYL/RCAR Receptors Play a Vital Role in the Abscisic-Acid-Dependent Responses of Plants to External or Internal Stimuli.

Abscisic acid (ABA) is a phytohormone that plays a key role in regulating several developmental processes as well as in response to stressful conditions such as drought. Activation of the ABA signaling cascade allows the induction of an appropriate physiological response. The basic components of the ABA signaling pathway have been recognized and characterized in recent years. Pyrabactin resistance, pyrabactin resistance-like, and the regulatory component of ABA receptors (PYR/PYL/RCAR) are the major components responsible for the regulation of the ABA signaling pathway. Here, we review recent findings concerning the PYR/PYL/RCAR receptor structure, function, and interaction with other components of the ABA signaling pathway as well as the termination mechanism of ABA signals in plant cells. Since ABA is one of the basic elements related to abiotic stress, which is increasingly common in the era of climate changes, understanding the perception and transduction of the signal related to this phytohormone is of paramount importance in further increasing crop tolerance to various stress factors.

Signal Transduction in Cereal Plants Struggling with Environmental Stresses: From Perception to Response.

Cereal plants under abiotic or biotic stressors to survive unfavourable conditions and continue growth and development, rapidly and precisely identify external stimuli and activate complex molecular, biochemical, and physiological responses. To elicit a response to the stress factors, interactions between reactive oxygen and nitrogen species, calcium ions, mitogen-activated protein kinases, calcium-dependent protein kinases, calcineurin B-like interacting protein kinase, phytohormones and transcription factors occur. The integration of all these elements enables the change of gene expression, and the release of the antioxidant defence and protein repair systems. There are still numerous gaps in knowledge on these subjects in the literature caused by the multitude of signalling cascade components, simultaneous activation of multiple pathways and the intersection of their individual elements in response to both single and multiple stresses. Here, signal transduction pathways in cereal plants under drought, salinity, heavy metal stress, pathogen, and pest attack, as well as the crosstalk between the reactions during double stress responses are discussed. This article is a summary of the latest discoveries on signal transduction pathways and it integrates the available information to better outline the whole research problem for future research challenges as well as for the creative breeding of stress-tolerant cultivars of cereals.

Abscisic Acid-Enemy or Savior in the Response of Cereals to Abiotic and Biotic Stresses?

Abscisic acid (ABA) is well-known phytohormone involved in the control of plant natural developmental processes, as well as the stress response. Although in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) its role in mechanism of the tolerance to most common abiotic stresses, such as drought, salinity, or extreme temperatures seems to be fairly well recognized, not many authors considered that changes in ABA content may also influence the sensitivity of cereals to adverse environmental factors, e.g., by accelerating senescence, lowering pollen fertility, and inducing seed dormancy. Moreover, recently, ABA has also been regarded as an element of the biotic stress response; however, its role is still highly unclear. Many studies connect the susceptibility to various diseases with increased concentration of this phytohormone. Therefore, in contrast to the original assumptions, the role of ABA in response to biotic and abiotic stress does not always have to be associated with survival mechanisms; on the contrary, in some cases, abscisic acid can be one of the factors that increases the susceptibility of plants to adverse biotic and abiotic environmental factors.

Proteomic analysis of S-nitrosylated and S-glutathionylated proteins in wheat seedlings with different dehydration tolerances.

A loss of dehydration tolerance in wheat seedlings on the fifth day following imbibition is associated with a disturbance in cellular redox homeostasis, as documented by a shift of the reduced/oxidized glutathione ratio to a more oxidized state and a significant increase in the ratio of protein thiols to the total thiol group content. Therefore, the identification and characterization of redox-sensitive proteins are important steps toward understanding the molecular mechanisms of the loss of dehydration tolerance. In the present study, proteins that were differentially expressed between fully turgid (control), dehydrated tolerant (four-day-old) and dehydrated sensitive (six-day-old) wheat seedlings were analysed. Protein spots having at least a significant (p < 0.05) two-fold change in protein abundance were selected by Delta2D as differentially expressed, identified by MALDI-TOF and LC-MS/MS, and classified according to their function. The observed changes in the proteomic patterns of the differentially S-nitrosylated and S-glutathionylated proteins were highly specific in dehydration-tolerant and -sensitive wheat seedlings. The metabolic function of these proteins indicates that dehydration tolerance is mainly related to nucleic acids, protein metabolism, and energy metabolism. It has been proven that leaf-specific thionins BTH6 and DB4, chloroplastic 50S ribosomal protein L16, phospholipase A1-II delta, and chloroplastic thioredoxin M2 are both S-nitrosylated and S-glutathionylated upon water deficiency. Our results revealed the existence of interplay between S-nitrosylation and S-glutathionylation, two redox-regulated protein posttranslational modifications that could enhance plant defence mechanisms and/or facilitate the acclimation of plants to unfavourable environmental conditions.

Maize proteomic responses to separate or overlapping soil drought and two-spotted spider mite stresses.

MAIN CONCLUSION: In maize, leaf proteome responses evoked by soil drought applied separately differ from those evoked by mite feeding or both types of stresses occurring simultaneously. This study focuses on the involvement of proteomic changes in defence responses of a conventional maize cultivar (Bosman) to the two-spotted spider mite infestation, soil drought and both stresses coexisting for 6 days. Under watering cessation or mite feeding applied separately, the protein carbonylation was not directly linked to the antioxidant enzymes' activities. Protein carbonylation increased at higher and lower SOD, APX, GR, POX, PPO activities following soil drought and mite feeding, respectively. Combination of these stresses resulted in protein carbonylation decrease despite the increased activity of all antioxidant enzymes (except the CAT). However, maize protein network modification remains unknown upon biotic/abiotic stresses overlapping. Here, using multivariate chemometric methods, 94 leaf protein spots (out of 358 considered; 2-DE) were identified (LC-MS/MS) as differentiating the studied treatments. Only 43 of them had individual discrimination power. The soil drought increased abundance of leaf proteins related mainly to photosynthesis, carbohydrate metabolism, defence (molecular chaperons) and protection. On the contrary, mite feeding decreased the abundance of photosynthesis related proteins and enhanced the abundance of proteins protecting the mite-infested leaf against photoinhibition. The drought and mites occurring simultaneously increased abundance of proteins that may improve the efficiency of carbon fixation, as well as carbohydrate and amino acid metabolism. Furthermore, increased abundance of the Rubisco large subunit-binding protein (subunit ß), fructose-bisphosphate aldolase and mitochondrial precursor of Mn-SOD and decreased abundance of the glycolysis-related enzymes in the mite-free leaf (in the vicinity of mite-infested leaf) illustrate the involvement of these proteins in systemic maize response to mite feeding.

A triticale water-deficit-inducible phytocystatin inhibits endogenous cysteine proteinases in vitro.

Water-deficit is accompanied by an increase in proteolysis. Phytocystatins are plant inhibitors of cysteine proteinases that belong to the papain and legumain family. A cDNA encoding the protein inhibitor TrcC-8 was identified in the vegetative organs of triticale. In response to water-deficit, increases in the mRNA levels of TrcC-8 were observed in leaf and root tissues. Immunoblot analysis indicated that accumulation of the TrcC-8 protein occurred after 72h of water-deficit in the seedlings. Using recombinant protein, inhibitory activity of TrcC-8 against cysteine proteases from triticale and wheat tissues was analyzed. Under water-deficit conditions, there are increases in cysteine proteinase activities in both plant tissues. The cysteine proteinase activities were inhibited by addition of the recombinant TrcC-8 protein. These results suggest a potential role for the triticale phytocystatin in modulating cysteine proteinase activities during water-deficit conditions.